The Geology of Denton County

" Nodosaria texana (plate 15). This species belongs to the lowest group of the animal kingdom known as the Protozoa and is the largest of these animals found in these rocks, all the others are microscopic and reference to them is reserved for the section on micrology. This species averages about one-half inch in length and when present in abundance is readily observed by the collector. Its zone of abundance in Denton County is in the upper part of the Weno, although it is well to mention that in southern and western Texas this species appears in a zone of abundance in the Del Rio clay, which corresponds in Denton County to the lower part of the Grayson. In Denton County the Grayson contains this species only rarely and then only as occasional isolated individuals.

  Ostrea quadriplicata (plate 8). In Denton County this species occurs occasionally in the Weno but reaches the zone of abundance in the lower part of the Pawpaw. Specimens vary somewhat due to the original environmental influences but the majority have the typical four-angle appearance which gives the species its name.

  Trigonia clavigera (plate 8). This species reaches a zone of abundance in the blue-gray shale near the middle of the Weno formation in Denton County. This abundance is only a relative one as this species is not as common as most of the others listed here and is included merely because the preservation in these blue shales is usually very fine and specimens, when encountered, are striking and attract the attention of even the casual collector.

  Pecten georgetownensis (plate 10). This is representative of an interesting group of "split rib" pectens found in the Weno over a large area. Note the groove present in the rib. Even small fragments are diagnostic and of value in establishing the stratigraphy of a new exposure.

  Gervilliopsis [Gervillia] invaginata (plate 9). This is a species which belongs to a group related to the modern "razor" clams. It occurs in the lower Weno in Denton County in a zone of great abundance, the individuals being compressed against each other in a clay layer several feet thick. In spite of the abundance, good specimens which are nearly entire, are difficult to find. In fresh cuts and exposures of this clay member, these razor clams have a shiny silvery appearance and are known in Denton and Cooke counties by the local name of "petrified sardines."

  Schloenbachia wintoni (plate 5). This small ammonite averaging rather less than six inches in diameter, marks the Weno throughout North Texas. It is rather difficult for the untrained person to distinguish this from certain other small ammonites, especially certain ones occurring in the Duck Creek, but a superficial distinction for this species is the presence of the notched tubercle at the outer end of each rib. In some cases in the Weno shales in Denton and Cook counties this ammonite is found pre-served in the original nacreous shell and not as a mud cast. In this case the notched effect of the outer tubercles is obscured by the shell.   "

The Geology of Tarrant County

"Brief Diagnosis: The Weno formation consists of a series of limestones and brown or yellow calcareous marls containing seams of limestone or ironstone, lying above the Gryphea conglomerate of the top of the Denton marl, and below the Pawpaw clays. It is 67 feet thick on Sycamore Creek near Fort Worth and nearly twice as thick at the Red River. In Tarrant County it is reduced in thickness but it is not in any way "consolidated" (with the adjoining formations) as has been claimed. It is abundantly fossiliferous. "

The Geology of Texas - Vol. 1

WENO FORMATION

Nomenclature.—Hill (788, p. 329) used the term "North Denison sands" for all strata between the top of the Denton Gryphaea shell aggregate and the base of the Pawpaw formation. Taff (1575, p. 273) used for the Weno the term "Denison" marl, a name preoccupied for the "Denison subgroup" in Hill's earlier papers. The term "Weno subgroup" was used by Hill (803, pp. 269-271, 274 ff.) to include the Weno and Pawpaw formations, and the term Weno formation (803, p. 275) for the same strata as his original North Denison sands (his beds j-m) . It is in this last sense that later writers have used the term Weno. The type locality is near the abandoned village of Weno, on Red River about 5 miles northeast of Denison.

Stratigraphic position and contacts.—Stephenson (1530, p. 142) records that in the Saint Louis and San Francisco Railway cut, 3/4 mile north of the Union Station at Denison, the basal 3 to 12 inches of the 2-foot Quarry limestone is conglomeratic, containing scattered pebbles of water worn calcareous sandstone, sandy lime-stone, and calcareous and ferruginous concretions, the largest 3 inches or more in length. A few borings filled with characteristic Quarry limestone material occur in the top of the underlying Weno clay, and otherwise the Quarry overlies the Weno with a sharply defined contact. In the absence of contrary evidence, this indicates that the Quarry is better classified with the Pawpaw beds. In Tarrant County this contact shows a sharp lithologic break, but no other evidences of unconformity are reported. The Denton-Weno contact is concordant and may be conformable.

Facies.—In the Denison, the southern Oklahoma, and the El Paso sections, the Weno is somewhat sandy. Its sediments in general are marl and limestone, of the neritic facies, with ironstone and ferruginous concretions. Near Fort Stockton a thin interfingering of Toucasia reef limestone occurs.

Areal outcrop; local sections.—In Love County, Oklahoma, the Weno consists of dark blue clay with many ironstone and ferrruginous sandy clay concretions, and segregations of mineral salts. It contains fossils, nacreous, and in the form of ironstone casts and impressions. It is 90 feet thick in southwestern part of Marshall County, and 135 feet thick in the northern part. Here the Weno contains many thin soft sandy layers and clay ironstone concretions. The northward increase in thickness is mostly in the sandy layers, which on the south limb of the Preston anticline average only 2 inches in thickness, but on the north limb, as at a locality 3 miles east of Kingston, are several feet in thickness. The sandy, ferruginous Quarry limestone maintains a thickness of 2 to 3 feet in this area. Several similar indurated layers occur in the lower Pawpaw; and in the Weno, 20 to 30 feet below the Quarry, there is a persistent hard, sandy limestone about a foot thick, weathering yellowish-white and resembling the Quarry. In Grayson County, there is about 117 feet of the Weno, consisting principally of clay; it is composed of dark gray shaly clay with subordinate thin partings, lenses and layers of fine, gray-to-yellow sand and sandstone, and, in the upper part, many small flattish ferruginous concretions and some small marcasite concretions. On the north limb of the Preston anticline, in the left bank of Washita River, 2¾ miles west of Platter, Oklahoma, there is a layer of sandstone 5 or 6 feet below the Quarry limestone and several layers of thin flaggy sandstone (25 to 40 feet below the Quarry. On the north limb of the anticline, in Marshall County, the Weno is 135 feet thick (1530, p. 141). At level about 44 feet above the base, in Duck Creek, north of Denison, there is a layer of large (4 to 5 feet in diameter) indurated and laminated ironstone concretions ("niggerheads"). Above these the nacreous ammonites (Engonoceras serpentinum) are most abundant. In the upper 50 feet of the formation, as seen in cuts a mile north of Denison, there are many nacreous shells (Turritella, Nucula, Yoldia, Corbula, and others).

In Cooke County the Weno is 100 feet thick. In Denton Creek, east of Justin, the upper 42 feet is exposed; in the northern part of the county near Sanger it is 105 feet thick, and in the southern part, west of Roanoke, 66 feet thick. On Clear Creek, Hill records 81 feet of Weno (803, p. 275) ; limestone seams are already appearing in this section.

In the Tarrant County section of the Weno, limestone is the dominant material. The formation is 67 feet thick. The basal 15 feet is a blue clay, capped by two marly limestone ledges, containing Gervilliopsis and other fossils. This portion is very fossiliferous, and locally contains a zone of abundance of Turritella wenoensis (T. ventrivoluta Cragin?) and Pecten georgetownensis Kniker. The medial portion consists of 34 feet of marl and some soft limestone, with Haplostiche texana (Conrad) in its upper part. The upper 18 feet beneath the Pawpaw is medium-bedded, marly, grayish-white limestone, with subordinate marl layers, containing Macraster obesus Adkins and other fossils; it makes a distinct bench. These portions of the Weno are well exposed on Sycamore Creek. The Quarry limestone is not recognizable. In Johnson County 40 to 50 feet of Weno occurs. The upper one-half is mostly limestone, with subordinate marl seams, containing Pervinquieria wintoni, Pecten georgetownensis, Haplostiche texana, and other local markers. The lower one-half is marl with limestone seams. In McLennan and Bell counties it is reduced to 20 to 30 feet, and consists of limestone in thin to medium beds with slight marl interbedding. At Austin (803, p. 265) the Weno is probably represented by less than 10 feet of limestone (Hill's bed 6, on sect 29) . South of Austin it has not been traced.

At Fort Stockton, the Weno, lying between the middle and upper cap rocks, is represented by 81 feet of marly limestone, marl, yellowish sandy limestone, and sandy marl. These strata contain a prominent ferruginous flint layer near their top. Fossils are: Haplostiche texana, Pervinquieria aft. wintoni, and a zone of Toucasia in a thin reef limestone finger near the middle. The section at Kent is similar. At El Paso the Weno is blue clay basally, with pyritic micromorphs (Pervinquieria n. spp., Neokentroceras?), and sandy clay above, with Alectryonia quadriplicata.

Paleontology.—In the upper Washita, as in the upper Albian, quadrituberculate Pervinquieria (P. wintoni group) appear. Several species are known from the Denton onwards: P. wintoni is wide-spread in the Weno and is a practical marker; new species of the P. kiliani group occur; Prohysteroceras occurs; Macraster obesus is a practical marker.

Miss M. J. Rathbun has identified from Weno material in the Bureau of Economic Geology the following macrourous crustacea: Enoploclytia n.sp., Palaeastacus walkeri (Whitfield) ; the latter species occurs also in the Fort Worth formation and in the Fort Worth portion of the Georgetown.